Diving computers are commonly used by divers to monitor key parameters, such as remaining air, present depth, compass (direction), etc. Divers rely on their diving computers and usually turn to the surface when there is a certain air pressure left in the tank, such as 50-100 bar. In modern systems, pressure information may be sent wirelessly from a tank sensor unit to the diving computer using electromagnetic induction or other near-field communication systems that are operable at short distances under water. U.S. Pat. No. 8,275,311, U.S. Pat. No. 7,650,208, U.S. Pat. No. RE42218 and FI 20135911 disclose underwater transceiver systems of this kind.
Despite advanced personal equipment, scuba diving accidents occur. The most common triggers for these are insufficient gas, entrapment and equipment problems. It is thus clear that there is not only important to monitor one's own key parameters when diving, but it would serve an important purpose to monitor the key parameters of all participating divers, to prevent accidents from happening.
It is well known that the most favorable method of wireless underwater communication is done by acoustic means. Sound travels extremely well underwater, and can be encoded to contain data. Scuba divers are sometimes seen using full face masks equipped with wireless voice communication systems. These communication systems rely on ultrasonic sound waves to transfer encoded voice from one diver to another, or to a receiving station on the surface. Unfortunately, existing ultrasonic communication systems are typically bulky and expensive.
In US2014048069 is provided a method for monitoring a group of divers with a plurality of transmitter devices, each transmitter device being connected to receive a tank pressure from a regulator a diver. The transmitter device generates on/off-modulated sonic data packets, comprising e.g. an identification portion and a pressure indicating portion. A receiver device will then receive the sonic data packets. Additionally, the direction to the source may be calculated and displayed by means of calculating the phase shift between the signals received on various transducers in the receiver device. This provides for a bilateral point-to-point indication between two transducers, and provides thus no communication for overall positioning of a group of divers. In fact, the simple modulation technique used will result in that multiple user communication will frequently cause collisions between data packets, effectively corrupting them.
In WO 2014/075860 is described a solution for determining the absolute position of a diver. The system has a diving base with a GPS receiver and an underwater acoustic modern configured to retransmit GPS coordinates under water. Combining retransmitted GPS coordinates with a calculated direction and distance to the base unit provides the diver with his or her absolute position. The diver equipment has several microphones to detect the direction to the base, and a pairing of the base and diver equipment is made to make it possible to calculate the distance between the equipment. This system also supports sharing of position and other data between paired divers via the (unmanned) base. The underwater network is based on a time-division multiplex scheme, which is sensitive to multipath propagation and allows for only slow data rates, in a situation which requires a lot of GPS information signaling between the various devices. In addition, as the position calculation is done by each diver's equipment and sent via the base unit, position calculation errors will accumulate in the relative position between two divers.
Generally speaking, underwater transmission of sound requires relatively high voltages to achieve acceptable ranges. To achieve the required change of several hundred meters, a transducer such as a typical ring transducer must be excited by a square wave of between 100V and 200V. Even higher voltages are possible (300-1000V) and will increase the range further, at the cost of reduced battery life. Generating such a high voltage from a small battery is complicated, and requires a large inductor and one or more large capacitors. Fitting pressure transducers, electronic circuit boards, batteries and large inductors and capacitors into a small housing in a diver's equipment is a major challenge. Therefore, there is a need for simple devices that can be kept small and have a low energy consumption. There is also a need for improved communication systems and devices in particular for positioning the individuals in a team.